Device and method for fan speed control

ABSTRACT

The present disclosure describes devices and methods that include a heartbeat signal for detecting an abnormality in the control of a fan for an electronic system. A fan controller can assume control of a fan over a fan speed control circuit in response to the abnormality. Control of the fan by the fan controller can eliminate or reduce overheating within the system caused by improper fan speed, in response to the abnormality.

FIELD OF THE INVENTION

The present invention relates to cooling fans, and more specifically, tothe control of a cooling fan in response to the lack of a controlsignal.

BACKGROUND

Fans are often required in various electronic systems that generate heatto cool the systems. The speed of the fan typically is controlled by afan speed control circuit. For example, in computer systems, such asserver systems, there often is a baseboard management controller (BMC)that generates a fan speed control signal. The fan speed control signalis then sent to a fan controller within a fan module. The fan controllerdynamically controls the fan speed based on the fan speed control signalto cool the computer system, in addition to saving power consumption andreducing noise.

In the event that the hardware, firmware, or software of the fan speedcontrol circuit fails (for example, in the BMC), the fan may stopaltogether, or keep running at a constant speed that is insufficient forcooling the electronic system. This can lead to the electronic systemhanging due to overheating. In a worst case scenario, improper fan speedcontrol can even lead to permanent damage to the system.

Accordingly, there is a need for devices and methods that overcome theforegoing drawbacks.

SUMMARY

The various embodiments concern devices and methods for controlling afan in the event of an abnormality in the normal control of the fan.

The various embodiments further concern a heartbeat signal that ismonitored by a fan controller. In the event of a discrepancy in theheartbeat signal, the fan controller assumes control over the fan.

A method of controlling a fan within an electronic system, according toa first embodiment, includes monitoring a heartbeat signal. Theheartbeat signal indicates the normal operation of the electronicsystem. The method further includes detecting a discrepancy in theheartbeat signal based on the monitoring. The method also includescontrolling the fan according to a safe fan speed in response to thediscrepancy.

In some implementations, the heartbeat signal can be generated by a fanspeed control circuit of the electronic system. In which case, theheartbeat signal indicates normal operation of the fan speed controlcircuit.

In some implementations, the electronic system can be a computer system,and the fan speed control circuit can be a baseboard managementcontroller.

In some implementations, the method can also include setting the safefan speed by the fan speed control circuit prior to detecting thediscrepancy.

In some implementations, the safe fan speed can be less than full speed,or can be full speed.

In some implementations, the safe fan speed can be set at startup of thecomputer system, at reset of the computer system, or both.

In some implementations, the heartbeat signal can be periodic; and thediscrepancy can be a lack of the heartbeat signal during at least oneperiod, during two or more sequential periods, or during two or morenon-sequential periods.

In some implementations, the heartbeat signal can be embedded within afan speed control signal.

In some implementations, the method can include determining that thediscrepancy in the heartbeat signal has not been corrected, andcontinuing the controlling of the fan according to the safe fan speed inresponse to the determination.

A method of controlling a fan module for cooling a computer system,according to a second embodiment, includes a fan speed control circuitof the computer system generating a fan speed control signal that isbased on one or more parameters corresponding to heat generated withinthe computer system. The method further includes the fan speed controlcircuit generating a heartbeat signal indicating normal operation of thefan speed control circuit. The method also includes a fan controller ofthe fan module controlling a speed of a fan of the fan module based onthe fan speed control signal. The method additionally includes the fancontroller monitoring the heartbeat signal. The method also includes thefan controller detecting a discrepancy in the heartbeat signal based onthe monitoring. The method further includes the fan controllercontrolling the speed of the fan based on a safe fan speed, in place ofthe fan speed control signal in response to the discrepancy.

In some implementations, the method includes the fan controllerdetermining that the discrepancy in the heartbeat signal has not beencorrected; and the fan controller continuing the controlling of the fanaccording to the safe fan speed in response to the determination.

In some implementations, the method includes the fan controllerdetermining that the discrepancy in the heartbeat signal has beencorrected; and the fan controller resuming control of the fan accordingto the fan speed control signal in response to the determination.

In some implementations, the method includes setting the safe fan speed,by the fan speed control circuit, prior to the fan controller detectingthe discrepancy.

In some implementations, the safe fan speed is full speed.

An electronic system, according to the third embodiment, includes a fanspeed control circuit configured to generate a heartbeat signalindicating normal operation of the fan speed control circuit. The systemalso includes a fan module having a fan controller and a fan. The fancontroller is configured to detect a discrepancy in the heartbeatsignal, and control the fan according to a safe fan speed in response tothe discrepancy.

In some implementations, the electronic system can be a computer system,and the fan speed control circuit can be a baseboard managementcontroller. The baseboard management controller can be configured to setthe safe fan speed prior to the fan controller detecting thediscrepancy. The safe fan speed is less than full speed. Further, thesafe fan speed can be set at startup of the computer system, at reset ofthe computer system, or both.

In some implementations, the heartbeat signal can be periodic; and thediscrepancy can be a lack of the heartbeat signal during at least oneperiod, during two or more sequential periods, or during two or morenon-sequential periods.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure, and its advantages and drawings, will be betterunderstood from the following description of exemplary embodimentstogether with reference to the accompanying drawings. These drawingsdepict only exemplary embodiments, and are therefore not to beconsidered as limitations on the scope of the various embodiments orclaims.

FIG. 1 illustrates a schematic view of an electronic system forcontrolling a fan module with a heartbeat signal, according to aspectsof the present disclosure.

FIG. 2 illustrates a process for controlling a fan module within anelectronic system, according to aspects of the present disclosure.

FIG. 3 illustrates a process for setting a safe fan speed, according toaspects of the present disclosure.

FIG. 4 illustrates a process for controlling a fan module for cooling acomputer system, according to aspects of the present disclosure.

DETAILED DESCRIPTION

The various embodiments are described with reference to the attachedfigures, where like reference numerals are used throughout the figuresto designate similar or equivalent elements. The figures are not drawnto scale, and they are provided merely to illustrate the instantinvention. It should be understood that numerous specific details,relationships, and methods are set forth to provide a fullunderstanding. One having ordinary skill in the relevant art, however,will readily recognize that the various embodiments can be practicedwithout one or more of the specific details, or with other methods. Inother instances, well-known structures or operations are not shown indetail to avoid obscuring certain aspects of the various embodiments.The various embodiments are not limited by the illustrated ordering ofacts or events, as some acts may occur in different orders and/orconcurrently with other acts or events.

To that extent, elements and limitations that are disclosed, forexample, in the Abstract, Summary, and Detailed Description sections,but not explicitly set forth in the claims, should not be incorporatedinto the claims, singly, or collectively, by implication, inference, orotherwise. For purposes of the present detailed description, unlessspecifically disclaimed, the singular includes the plural and viceversa. The word “including” means “including without limitation.”Moreover, words of approximation, such as “about,” “almost,”“substantially,” “approximately,” and the like, can be used herein tomean “at,” “near,” or “nearly at,” or “within 3-5% of,” or “withinacceptable manufacturing tolerances,” or any logical combinationthereof, for example.

The present disclosure describes devices and methods that include aheartbeat signal generated by a fan speed control circuit. The heartbeatsignal is monitored by a fan controller within a fan module. When thefan controller detects that the heartbeat signal has stopped, or detectsany other type of discrepancy indicating an abnormality, the fancontroller takes over control of the fan speed. Specifically, the fancontroller operates the fan at a safe fan speed to keep the systemassociated with the fan cool despite the abnormality.

FIG. 1 illustrates a schematic view of an electronic system 100 forcontrolling a fan module 102 with a heartbeat signal, according toaspects of the present disclosure. Although the present disclosure isprimarily directed to computer systems, such as server systems, theelectronic system 100 can be within any type of system that generatesheat during use and that uses a fan to dissipate the heat. Moreover, theelectronic system 100 of FIG. 1 can be for the entire system. Forexample, the electronic system 100 can be an overall server system, andthe fan 108 (described below) can be for cooling the overall system.Alternatively, the electronic system 100 of FIG. 1 can be a componentelectronic system within a larger system. For example, the electronicsystem 100 can be a power unit, a graphics processing component, acentral processing component, or the like within a computer system; andthe fan 108 (described below) can be for cooling the specific component.

The electronic system 100 includes the fan module 102 and a fan speedcontrol circuit 104. The fan module 102 includes a fan controller 106and a fan 108. The fan speed control circuit 104 is separate from thefan module 102. In the context of computer systems, the fan speedcontrol circuit 104 can be located on the motherboard. The fan speedcontrol circuit 104 has access to and monitors one or more parameters ofthe electronic system 100. The parameters relate to the heat that isgenerated within the electronic system 100. From the parameters, the fanspeed control circuit 104 determines the amount of cooling needed forthe system 100. Based on the amount of cooling needed, the fan speedcontrol circuit 104 generates a fan speed control signal. In the contextof a server system, the fan speed control circuit can be a BMC. The BMCmonitors parameters of the server system that relate to how much heat isbeing generated, and translates that information into the generated fanspeed control signal. For example, the parameters can be processor,memory, and/or internal chassis temperatures. The fan speed controlcircuit 104 can generate the fan speed control signal based on hardware,firmware, software, or a combination thereof. The fan speed controlsignal can be any type of digital or analog signal. In one or moreembodiments, the fan speed control signal can be a pulse widthmodulation signal.

The fan speed control circuit 104 is communicatively connected to thefan controller 106 of the fan module 102 via a connection 110. Theconnection 110 can be one or more wired connections, one or morewireless connections, or one or more wired and wireless connections. Thefan speed control circuit 104 communicates the fan speed control signalto the fan controller 106 via the connection 110. In response to the fanspeed control signal, the fan controller 106 operates the fan 108 at theinstructed speed.

In one or more embodiments, the fan controller 106 can generate a fanoperation signal and communicate the fan operation signal back to thefan speed control circuit 104. The fan operation signal can verify thatthe fan 108 is operating as instructed by the fan speed control circuit104. In one or more embodiments, the fan operation signal can be atachometer signal that reports the number of revolutions of the fan.Based on the number of revolutions, the fan speed control circuit 104can verify that the fan 108 is operating at the appropriate speed orduty cycle.

According to the present disclosure, the fan speed control circuit 104also generates a heartbeat signal and transmits the heartbeat signal tothe fan controller 106. The heartbeat signal indicates normal operationof the fan speed control circuit. The fan controller 106 can thenmonitor for the heartbeat signal to determine whether there is anyabnormality with the fan speed control circuit 104, or any othercomponent of the electronic system 100 that may be affecting the fanspeed control circuit 104. The heartbeat signal can be a continuous orperiodic signal. In one or more embodiments, the heartbeat signal can betransmitted (embedded) within the fan speed control signal or can betransmitted as a separate signal. In one or more embodiments, theheartbeat signal can be transmitted over the same wired and/or wirelessconnection as the fan speed control signal and/or fan operation signal.Alternatively, the heartbeat signal can be transmitted over a differentwired or wireless connection than the fan speed control signal and thetachometer signal.

For example, in one embodiment, the connection 110 can be a five-pingeneral purpose output pin connection. Two of the five pins can providea common ground and a voltage supply (e.g., a nominal+12 Volts) to thefan module 102. The third pin can provide the fan speed control signalto the fan controller 106. The fourth pin can provide the fan operationsignal from the fan controller 106 back to the fan speed control circuit104. The fifth pin can be added to provide the heartbeat signal from thefan speed control circuit 104 to the fan controller 106.

However, in one or more embodiments, the connection 110 can vary frombeing a five-pin connection. For example, the connection 110 can be afour-pin connection, and the heartbeat signal can be provided via one ofthe other four pins. In one embodiment, the heartbeat signal can be aspecific, periodic pulse-width modulation within the fan speed controlsignal that does not affect the speed of the fan; or negligibly affectsthe speed of the fan. For example, the specific, periodic pulse-widthmodulation can be a short positive (or negative) square wave immediatelyfollowed by a short negative (or positive) square wave that occursaccording to a specific period. In which case, the two waves effectivelynegate each other with respect to changing the speed of the fan.However, the fan controller 106 can monitor for the specific, periodicpulse-width modulation within the fan speed control signal as theheartbeat signal. In such embodiments, a conventional connection betweenthe fan speed control circuit 104 and the fan controller 106 can be usedwithout having to add a fifth pin. However, other types of connectionsfor the connection 110 are possible than those described above. Suchother connections include, for example, a platform environment controlinterface (PECI) bus, an inter-integrated circuit (I²C) bus, and thelike. In the case of the PECI bus and the I²C bus, the safe fan speedsignal can be a command sent from the fan speed control circuit 104 tothe fan controller 106.

The generation and transmittal of the heartbeat signal from the fanspeed control circuit 104 to the fan controller 106 indicates that theelectronic system 100 is operating normally with respect to control ofthe fan 108. Accordingly, the fan controller 106 within the fan module102 monitors for a discrepancy in the heartbeat signal. A discrepancycan be the lack of the continuous heartbeat signal, the lack of theheartbeat signal during one period, or the lack of the heartbeat signalduring two or more sequential or non-sequential periods.

When the fan controller 106 detects a discrepancy in the heartbeatsignal, the fan controller 106 takes over control of the speed of thefan 108 from the fan speed control circuit 104. When the fan controller106 takes over control of the fan 108, the fan controller 106 canoperate the fan 108 at a safe fan speed. In one or more embodiments, thesafe fan speed can be full speed to provide maximum cooling. In one ormore embodiments, the safe fan speed can less than full speed. In one ormore embodiments, the safe fan speed can be a default speed set withinlogic of the fan controller 106 that cannot be changed. Alternatively,in one or more embodiments, the safe fan speed can be set by the fanspeed control circuit 104 any time before the discrepancy, such as atstartup or reset of the fan speed control circuit 104 or the electronicsystem 100. The fan speed control circuit 104 can send the safe fanspeed via the heartbeat signal, the fan speed control signal, or anyother signal during operation. Thus, in the event of an issue with thefan speed control circuit 104 controlling the fan 108 through the fancontroller 106, the heartbeat signal can prevent or reduce thelikelihood of the electronic system 100 hanging or being damaged as aresult of improper fan speed control. Instead, the fan controller 106can assume control of the fan speed to maintain cooling within thesystem 100.

FIG. 2 illustrates a process 200 for controlling a fan within anelectronic system, according to aspects of the present disclosure. Theprocess 200 can be performed by the fan speed control circuit 104 andthe fan controller 106 disclosed above (FIG. 1). The electronic systemcan be any electronic system, such as the electronic system 100,including a computer system, a sub-component within a computer system,or any other electronic system that uses a fan to dissipate generatedheat. The process 200 begins at step 202, where a fan controller of afan module monitors for a heartbeat signal. During normal operation, afan speed control circuit that monitors parameters that correspond tothe amount of heat generated by the electronic system generates theheartbeat signal. The heartbeat signal indicates normal operation of theelectronic system. In one or more embodiments, normal operation of theelectronic system includes the fan speed control circuit receiving theexpected parameters used to generate a fan speed control signal. In oneor more embodiments, normal operation also includes values of theparameters being within expected and/or predetermined ranges, such asnormal operating conditions. Normal operation also includes the fanspeed control circuit generating and outputting the fan speed controlsignal to the fan controller according to a predetermined scheme, suchas continuously or periodically. The fan module can be associated withthe cooling of any electronic system, such as a computer system or acomponent within a computer system. The heartbeat signal can becontinuous or periodic. In one or more embodiments, the heartbeat signalcan be a high/low toggling signal, a command/data signal, or acombination thereof.

At step 204, the fan controller of the fan module determines whether adiscrepancy exists in the heartbeat signal. The discrepancy can be thelack of the fan speed control signal. For example, with a continuous fanspeed control signal, the discrepancy can be the fan controller nolonger receiving the signal. As another example, with a periodic fanspeed control signal, the discrepancy can be the fan controller notreceiving the signal for one period, or not receiving the signal for twoor more sequential or non-sequential periods. As another example, for atoggling signal and/or a command data signal, the discrepancy can be anincorrect value within the signal. If a discrepancy does not exist, theprocess 200 loops back to step 202. If a discrepancy exists, the fancontroller of the fan module detects a discrepancy in the heartbeatsignal based on the monitoring, and the process 200 proceeds to step206.

At step 206, in response to the fan controller detecting a discrepancy,the fan controller controls the fan according to a safe fan speed. Thesafe fan speed is configured to keep the fan operating at a speed thatattempts to maintain the cooling of the electronic system, despite thelack of proper fan speed control by the fan speed control circuit. Inone or more embodiments, the safe fan speed can be a maximum operatingspeed of the fan (i.e., full speed). In one or more embodiments, thesafe fan speed can be less than the maximum operating speed but still asufficient amount that, on average, should minimize the buildup of heatwithin the electronic system. For example, in one embodiment, the safefan speed can be determined based on a worst case thermal simulation(e.g., CPU and memory running at full load), but still be less than fullspeed. In one embodiment, the safe fan speed can be pre-defined andfixed by thermal or system designer. The safe fan speed can be a defaultspeed set within logic of the fan controller. Alternatively, the safefan speed can be set by the fan speed control circuit prior to thediscrepancy, as discussed further with respect to the process 300 below.For example, the safe fan speed can be the maximum speed which the fanspeed control circuit sends to fan controller during normal systemoperation. The fan controller can record all fan speed requirements fromthe fan speed control circuit, and then update and keep the maximumspeed as the safe fan speed.

In one or embodiments, the process 200 ends after step 206, and the fancontroller controls the fan according to the safe fan speedindefinitely, or until power is cut from the fan module, the electronicsystem, or a combination thereof. In one or more embodiments, theprocess 200 optionally can proceed to step 208 where the fan controllerdetermines whether the discrepancy in the heartbeat signal has beencorrected. If the discrepancy has been corrected, the process 200 loopsback to step 202, and the fan controller continues monitoring theheartbeat signal. If the discrepancy has not been corrected, the process200 loops back to step 206, and the fan controller continues operatingthe fan according to the safe fan speed.

Based on the process 200, the heartbeat signal can prevent or reduce thelikelihood of the electronic system hanging or being damaged as a resultof improper fan speed control in the event of an issue with the fanspeed control circuit. The fan controller can detect a discrepancy inthe control of the fan speed via the heartbeat signal and take overcontrol from the fan speed control circuit. The fan controller assumingcontrol can reduce the likelihood of issues within the electronicsystem, in response to the buildup of heat.

In one or more embodiments, the fan controller can perform one or moreadditional or alternative functions in response to detecting adiscrepancy in the heartbeat signal. The one or more functions aid inpreventing the system from hanging, or being damaged, in response to thefan speed control circuit not being able to control the speed of thefan.

In one embodiment, the fan module can include an audible and/orelectronic alarm that is triggered when the fan controller detects adiscrepancy in the heartbeat signal. An alarm can alert an operator,technician, or the like, of the discrepancy. In response, the operator,technician, or the like can investigate the issue and take appropriateaction, such as shutting the system down and/or manually controlling thefan speed using a switch or other manual control device within the fanmodule.

In one embodiment, the fan controller can be communicatively coupled toa circuit within the system that allows the fan controller to initiateshutdown of the system. The fan controller shutting the system downfurther prevents damage to the system caused by the inability to controlthe fan speed. In one embodiment, the fan controller can communicate toone or more CPUs within the system to reduce the clock speeds of theCPUs to reduce the amount of heat that is generated. In one embodiment,the fan controller can be communicatively coupled to a circuit withinthe system that allows the fan controller to signal or control thesystem or other key components (e.g., memory modules (e.g., dual in-linememory modules or DIMMs), a network interface controller (NIC), astorage module, or other components) to slow down or reduce heat.

FIG. 3 illustrates a process 300 for setting a safe fan speed within anelectronic system, according to aspects of the present disclosure. Theprocess begins at step 302, where the fan speed control circuit startsor resets, and begins generating and transmitting the fan speed controlsignal to the fan module. As described above, the fan speed controlcircuit monitors parameters of the electronic system associated withheat generation to generate the fan speed control signal. Step 302 canoccur when the electronic system, such as the computer system, thatincludes the fan speed control circuit starts and/or resets.

At step 304, the fan speed control circuit sends the safe fan speed tothe fan module. In one or more embodiments, the fan speed controlcircuit can send the safe fan speed to the fan module via a heartbeatsignal, such as the heartbeat signal described in the process 200. Inone or more embodiments, the fan speed control circuit can send the safefan speed via another signal, such as the fan speed control signal. Thefan speed control circuit can send the safe fan speed once at startup orafter a reset, periodically or on demand, in response to a software,firmware, or hardware request. Thereafter, the fan module will have thesafe fan speed stored in logic in the event of a discrepancy in theheartbeat signal. The process 300 can occur before the process 200 hasinitiated or simultaneously with the process 200, once the fan moduleand the fan speed control circuit startup.

FIG. 4 illustrates a process 400 for controlling a fan module forcooling a computer system, according to aspects of the presentdisclosure. The process 400 can be performed by the fan speed controlcircuit 104 and the fan controller 106 disclosed above (FIG. 1). Theprocess 400 begins at step 402, when the fan speed control circuit ofthe computer system generates a fan speed control signal based on one ormore parameters corresponding to heat generated within the computersystem. As discussed above, the parameters can relate to, for example,one or more processor temperatures, one or more memory chiptemperatures, one or more ambient temperatures within the computersystem, or any other temperature associated with the computer system.The parameters can also relate to the amount of power consumed by thecomputer system, such as by the one or more processors, one or morememory chips, one or more power units, and the like.

At step 404, the fan speed control circuit generates a heartbeat signal.As discussed above, the heartbeat signal indicates normal operation ofthe fan speed control circuit.

In one embodiment, the process 400 can include step 405, where the fanspeed control circuit generates a safe fan speed and transmits the safefan speed to the fan controller, such as within the heartbeat signal.Alternatively, the fan speed control circuit can transmit the safe fanspeed with the fan speed control signal or another signal. Further,although described in relation to step 404, the fan speed controlcircuit can generate and transmit the safe fan speed to the fancontroller at any step or time prior to the step 410, such as when thefan speed control circuit starts or resets.

At step 406, the fan controller of the fan module controls the speed ofthe fan module based on the fan speed control signal generated andtransmitted by the fan speed control circuit. The fan speed controlcircuit 104 can transmit the fan speed control signal to the fancontroller via the connection 110, as described above. For example, theconnection 110 can include a general purpose output pin, and the fanspeed control circuit 104 can transmit the fan speed control signal viapulse-width modulation over the general purpose output in.

At step 408, the fan controller monitors the heartbeat signal generatedand transmitted by the fan speed control circuit. The fan speed controlcircuit 104 can transmit the heartbeat signal to the fan controller viathe connection 110, as described above. For example, the heartbeatsignal can be transmitted over the same general purpose output pin asthe fan speed control signal. In which case, the heartbeat signal can beembedded within the fan speed control signal. Alternatively, the fanspeed control circuit can transmit the heartbeat signal over a separategeneral purpose output pin of the connection, or any other connectiondisclosed herein.

At step 410, the fan controller detects a discrepancy in the heartbeatsignal based on the monitoring. The discrepancy can be the lack of theheartbeat signal, or any other variation in the heartbeat signal thatindicates an abnormality (or potential abnormality) of the fan speedcontrol circuit. For example, the discrepancy can be the lack of aperiodic heartbeat signal for one period, or for more than twosequential or non-sequential periods. The discrepancy can be any otherdiscrepancy disclosed above.

At step 412, the fan controller controls the speed of the fan based on asafe fan speed, in place of the fan speed control signal in response tothe discrepancy. As disclosed above, the safe fan speed can be fullspeed for maximum cooling. Alternatively, the safe fan speed can be lessthan full speed. In one or more embodiments, the safe fan speed can beset in the logic of the fan controller; or can be set based on the fancontroller having previously received the safe fan speed from the fanspeed control circuit prior to the discrepancy.

At step 414, the fan controller can optionally determine whether thediscrepancy in the heartbeat signal has been corrected. The fancontroller can perform the determination continuously, periodically, oron demand, such as in response to a software, firmware, or hardwarerequest. If the fan controller determines that the discrepancy in theheartbeat signal has been corrected, the process can loop back to step408. If the fan controller determines that the discrepancy in theheartbeat signal has not been corrected, the process can loop back tostep 412.

Based on the process 400, the computer system can control the fan modulefor cooling of the system. Further, in the event of an abnormality ofthe normal control, the lack of the heartbeat signal can prevent orreduce the likelihood of the computer system hanging or damaging one ormore components as a result of improper fan speed and temperaturecontrol.

While various embodiments of the present invention have been describedabove, it should be understood that they have been presented by way ofexample only, and not limitation. Numerous changes to the disclosedembodiments can be made in accordance with the disclosure herein withoutdeparting from the spirit or scope. Thus, the breadth and scope of thepresent invention should not be limited by any of the above describedembodiments. Rather, the scope of the invention should be defined inaccordance with the following claims and their equivalents.

Although the invention has been illustrated and described with respectto one or more implementations, equivalent alterations and modificationswill occur to others skilled in the art upon the reading andunderstanding of this specification and the annexed drawings. Inaddition, while a particular feature of the invention may have beendisclosed with respect to only one of several implementations, suchfeature may be combined with one or more other features of the otherimplementations as may be desired and advantageous for any given orparticular application.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting. As used herein, thesingular forms “a”, “an,” and “the” are intended to include the pluralforms as well, unless the context clearly indicates otherwise.Furthermore, to the extent that the terms “including”, “includes”,“having”, “has”, “with”, or variants thereof are used in either thedetailed description and/or the claims, such terms are intended to beinclusive in a manner similar to the term “comprising.”

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this invention belongs.Furthermore, terms, such as those defined in commonly used dictionaries,should be interpreted as having a meaning that is consistent with theirmeaning in the context of the relevant art and will not be interpretedin an idealized or overly formal sense unless expressly so definedherein.

What is claimed is:
 1. A method of controlling a fan within anelectronic system, comprising: monitoring a heartbeat signal indicatingnormal operation of the electronic system; detecting a discrepancy inthe heartbeat signal; and controlling the fan according to a safe fanspeed in response to the discrepancy.
 2. The method of claim 1, whereinthe heartbeat signal is generated by a fan speed control circuit of theelectronic system, and the heartbeat signal indicates normal operationof the fan speed control circuit.
 3. The method of claim 2, wherein theelectronic system is a computer system, and the fan speed controlcircuit is a baseboard management controller.
 4. The method of claim 2,further comprising setting the safe fan speed by the fan speed controlcircuit prior to detecting the discrepancy.
 5. The method of claim 4,wherein the safe fan speed is less than full speed.
 6. The method ofclaim 4, wherein the safe fan speed is set at startup of the computersystem, at reset of the computer system, or both.
 7. The method of claim1, wherein the heartbeat signal is periodic, and the discrepancy is alack of the heartbeat signal during at least one period, during two ormore sequential periods, or during two or more non-sequential periods.8. The method of claim 1, wherein the heartbeat signal is embeddedwithin a fan speed control signal or separate from the fan speed controlsignal.
 9. The method of claim 1, further comprising: determining thatthe discrepancy in the heartbeat signal has not been corrected andcontinuing the controlling of the fan according to the safe fan speed,in response to the determination.
 10. An electronic system comprising: afan speed control circuit configured to generate a heartbeat signalindicating normal operation of the fan speed control circuit; and a fanmodule comprising a fan controller and a fan, the fan controller beingconfigured to detect a discrepancy in the heartbeat signal and controlthe fan according to a safe fan speed, in response to the discrepancy.11. The electronic system of claim 10, wherein the electronic system isa computer system, and the fan speed control circuit is a baseboardmanagement controller.
 12. The electronic system of claim 11, whereinthe baseboard management controller is configured to set the safe fanspeed prior to the fan controller detecting the discrepancy.
 13. Theelectronic system of claim 12, wherein the safe fan speed is less thanfull speed.
 14. The electronic system of claim 12, wherein the safe fanspeed is set at startup of the computer system, at reset of the computersystem, or both.
 15. The electronic system of claim 10, wherein theheartbeat signal is periodic, and the discrepancy is a lack of theheartbeat signal during at least one period, during two or moresequential periods, or during two or more non-sequential periods.
 16. Amethod of controlling a fan module for cooling a computer system,comprising: generating, by a fan speed control circuit of the computersystem, a fan speed control signal based on one or more parameterscorresponding to heat generated within the computer system; generating,by the fan speed control circuit, a heartbeat signal indicating normaloperation of the fan speed control circuit; controlling, by a fancontroller of the fan module, a speed of a fan of the fan module basedon the fan speed control signal; monitoring, by the fan controller, theheartbeat signal; detecting, by the fan controller, a discrepancy in theheartbeat signal based on the monitoring; and controlling, by the fancontroller, the speed of the fan based on a safe fan speed in place ofthe fan speed control signal in response to the discrepancy.
 17. Themethod of claim 16, further comprising: determining, by the fancontroller, that the discrepancy in the heartbeat signal has not beencorrected; and continuing, by the fan controller, the controlling of thefan according to the safe fan speed in response to the determination.18. The method of claim 16, further comprising: determining, by the fancontroller, that the discrepancy in the heartbeat signal has beencorrected; and resuming, by the fan controller, controlling of the fanaccording to the fan speed control signal, in response to thedetermination.
 19. The method of claim 16, further comprising settingthe safe fan speed, by the fan speed control circuit, prior to the fancontroller detecting the discrepancy.
 20. The method of claim 16,wherein the safe fan speed is full speed.